The present invention relates to a method for manufacturing an expanded mesh sheet such as a latticed electrode for use in a battery and a manufacturing apparatus for carrying out the method.
As shown in FIG. 18, in an expanded mesh sheet, many strip-shaped lift portions (a) are connected with each other in a zigzag configuration by latticed connecting portions (b). An apparatus for manufacturing such an expanded mesh sheet is proposed in Japanese Patent Publication No. 60-29573.
According to this conventional art, as shown in FIGS. 15(a) and 15(b), a plurality of slits (c) are intermittently formed on a strip (A) in the longitudinal direction thereof in a first process. In this stage, the slits (c) are arranged in parallel with each other on the strip (A) and the strip-shaped lift portions (a) are formed by the adjacent slits (c). At this time, the strip-shaped lift portions (a) adjacent to each other in the widthwise direction of the strip (A) are bent in directions opposite to each other in approximately the thickness direction of the strip. A flat portion (d) is left extending in a widthwise direction between each adjacent group of slits.
As shown in FIG. 17, the first process is carried out by a first roll (g) comprising a plurality of disk-shaped cutters (f) having projections (e) provided at predetermined pitches in the periphery thereof and in groups in which the projections are superposed as spaced from one another by predetermined intervals in the axial direction of the roll, and a second roll (h). Each strip-shaped lift portion (a) is pressed against the projection (e) approximately in the thickness direction of the strip and is bent into a curved configuration between adjacent flat portions (d).
As shown in FIGS. 16(a) and 16(b), slits (i) for connecting slits (c) in adjacent groups thereof are formed in the flat portions (d) in a second process. Each slit (i) connects every other pair of adjacent slits (c) in the widthwise direction as extending through a flat portion (d). The portions of the strip (A) between the slits (i) adjacent to each other in the widthwise direction constitute the connecting portions (b).
The second process is performed by the second roll (h) and a third roll (j) as shown in FIG. 17. The third roll (j) comprises a plurality of superposed disk-shaped cutters (k), not having the projections (e) formed thereon. Reliefs (l) are provided at predetermined pitches alternately in the right and left sides at the periphery of the disk-shaped cutter (k). Similarly, reliefs (l) are provided in the disk-shaped cutter (f) of the second roll (h) and are opposed to the reliefs (l) of the disk-shaped cutter (k).
In the third process, the strip (A) having the strip-shaped lift portions (a) and the connecting portions (b) formed thereon is expanded widthwise as shown in FIG. 18.
However, the conventional art has the following drawbacks:
1. Slits are formed in two processes and the use of two rolls are necessary for each process. Therefore, time-taking adjustments such as the positioning of the rolls relative to one another and the rotating timing thereof are required to be made before starting an operation, and there is the possibility that a strip will be cut two times.
It is necessary to use three kinds of disk-shaped cutters and in addition, the disk-shaped cutter of the roll used in both processes is consumed in a short time by pressure applied thereto by the two rolls coacting therewith.
2. In shaping the strip, the strip-shaped lift portions are pressed by the top portion of the projection of the disk-shaped cutter and are pulled in the rotational direction of the disk-shaped cutter, with the result that tensile stress concentrates at the rear of the strip-shaped lift portion. In the conventional manufacturing apparatus, as shown in FIG. 19, each projection (e) is symmetrical with respect to a line extending radially of the disk-shaped cutter, and the top portion of each projection (e) is located centrally thereof with respect to the rotational direction of the disk-shaped cutter. Therefore, the length of the rear part of the strip-shaped lift portion (a) is only half of the whole length of the strip-shaped lift portion (a). Accordingly, the thickness of the rear part strip-shaped lift portion (d) is locally reduced and as such, it is likely to break when it is expanded.
3. According to the conventional apparatus, the thicknesses of the disk-shaped cutters (f) and (j) at the reliefs (l) are approximately constant therealong in a direction toward the outer peripheries of the cutters as shown in FIG. 20. Therefore, the disk-shaped cutters are likely to break at the bases of the reliefs (l) remote from the outer peripheries thereof. In particular, the disk-shaped cutters of the rolls used in the two processes are likely to be damaged by the pressure described in item 1 above.
4. As shown in FIG. 21, with the expansion of the strip in the widthwise direction thereof, the connecting portions (b) adjacent to each other in the widthwise direction are separated from each other widthwise, with the result that first, the strip-shaped lift portions (a) become twisted and then, each connection portion (b) rotates in a twist-removing direction. Thereafter, each strip-shaped lift portion (a) is bent with respect to the connecting portion (b) in the direction in which each strip-shaped lift portion (a) has been curved, with the result that the separation of the adjacent connecting portions (b) progresses.
As described above, according to the conventional art, the strip-shaped lift portions are twisted when the strip is initially expanded widthwise. Therefore, a great force is required to effect the expanding operation, so that the life of an apparatus for performing the expanding operation is relatively short.
This drawback is most remarkable when the thickness of the strip is large or the mesh is fine.